Among methods of obtaining a sufficient condensation heat even if the outside air temperature is low, a method of increasing a refrigeration capacity by heat recovery is known (e.g., see Patent Document 1). This method is implemented in a configuration including a main refrigerant circuit and a sub refrigerant circuit equipped with a second compressor, wherein the sub circuit recovers heat from the main circuit via an internal heat exchanger.
Among methods of efficiently supplying high-temperature water, a method of increasing water temperature by a two-stage compression cycle configuration (e.g., see the Patent Document 2). This method is implemented by letting water flow through a lower stage condenser and a higher stage condenser arranged in series.